The present invention relates to an automotive headlamp construction in which chromatic aberration is substantially eliminated.
An automotive headlamp converts light from a light source (bulb) into parallel rays so as to illuminate the road in front of the vehicle. Headlamps may be divided into two types: one in which the light from the light source is converted into generally parallel rays by a parabolic reflector, and another in which the light from the light source is converted into parallel rays by the combination of an elliptic reflector and a condenser lens.
The condenser lens used in the latter type tends to develop chromatic aberration since the rays incident upon a portion remote from the optical axis of the lens are subjected to higher refractive indices than in other areas. This chromatic aberration arises due to the fact that the light from the light source includes a variety of wavelengths (colors) for which the refractive index differs slightly. This in turn results in slightly different focal lengths of the lens for the different colors.
There have been a variety of conventional headlamps free from chromatic aberration, including a type in which a shade for diffusing light is disposed near the focal point of the reflector (Japanese Published Patent Application No. 53-23180) and a type in which a member for causing the light to refract or diffuse is directly fixed onto the surface of a condenser lens through an adhesive (Japanese Patent Preliminary Publication No. 60-62001).
However, these headlamps require the provision of, for example, a shade (mask) for diffusing and refracting the light to eliminate chromatic aberration, which shade must be specially worked or a powerful light source provided for overcoming the decrease in light transmissivity resulting from the members fixed to the condenser lens.